The present invention relates generally to a communication system, and in particular, the present invention relates to a method and apparatus for exchanging session initiation protocol signaling messages between a mobile station and a network for setup of multimedia calls.
Setup procedures associated with multimedia calls placed by mobile terminals are performed using a recently developed signaling protocol commonly known as the session initiation protocol (SIP). In particular, the session initiation protocol is an open internet protocol (IP) standard designed specifically for initiating, managing, and terminating interactive IP sessions, such as, but not limited to Voice over IP sessions and multimedia conferences.
A current method for utilizing the session initiation protocol involves a Global System for Mobile Communications (GSM) approach, which utilizes the slow dedicated control channel (SDCCH) for channel signaling for setting up and maintaining a call. However, the amount of data transmitted by the slow dedicated control channel is a relatively small amount, i.e., 23 bytes, and may occur approximately every 120 milliseconds, while session initiation protocol messages average approximately 400 bytes of information per message. As a result, the amount of time necessary to transport a multimedia message between a mobile station and a mobile terminal using the slow dedicated control channel is excessively long, since many slow dedicated control channels would be required to pass the session initiation protocol message to and from the mobile station. In addition, additional setup time would also be required in order to set up a signaling link if one is not already available.
Another method currently proposed for utilizing the session initiation protocol involves using packet data channels to set up and maintain a virtual multimedia connection. FIG. 1 is a data flow diagram of a session initiation protocol call setup sequence utilizing packet data channels. As illustrated in FIG. 1, prior to sending messages between a mobile station 100 and a network 102, a temporary block flow (TBF) 104 must be set up. When utilizing packet data channels to set up and maintain the virtual media connection, once temporary block flow 104 is set up between mobile station 100 and network 102, mobile station 100 transmits an INVITE command 106 to network 102 along a packet associated control channel (PACCH). Once network 102 receives INVITE command 106, a temporary block flow 108 is again set up between mobile station 100 and network 102, so that upon completion of the set up of temporary block flow 108, network 102 responds to INVITE command 106 by sending a RINGING status command 110 to mobile station 100 along the packet associated control channel.
Once RINGING status command 110 is sent, a temporary block flow 112 is once again set up between mobile station 100 and network 102 to enable transmission of an OK acknowledgement message 114 from network 102 to mobile station 100. Finally, a temporary block flow 116 is once again set up between mobile station 100 and network 102 to enable an acknowledge (ACK) message 118 to be sent from mobile station 100 to network 102.
FIG. 2 is a data flow diagram of an uplink temporary block flow set up sequence between a mobile station and a network. As illustrated in FIG. 2., during the set up of each of temporary block flows 104, 108, 112 and 116, mobile station 100 sends a channel request access burst 120 to network 102 using a random access channel (RACH). Network 102 responds by sending an immediate assignment message 122 along an access grant channel (AGCH) to mobile station 100. Mobile station 100 then sends a packet resource request message 124 along the packet associated control channel to network 102 requesting resources for the temporary block flow. Network 102 responds with a packet uplink assignment message 126, which is acknowledged by mobile station 100 in a packet control acknowledge message 128. Note that while the temporary block flow set up sequence shown in FIG. 2 is in the uplink direction, i.e., from mobile station 100 to network 202, a downlink temporary block flow set up sequence is similar, with the major exception being that network 102 initially pages mobile station 100.
Since a temporary block flow set up sequence can typically take approximately 1.7 seconds or more to complete, a relatively large amount of time is needed for set up of temporary block flows 104, 108, 112 and 116, so that the use of packet data channels to set up and maintain a virtual multimedia connection, as shown in FIG. 1, tends to require excessive set up times for multimedia calls as well.
As a result of the excessive call set up times required by current methods for utilizing session initiation protocols, excessive delays tend to occur when calls are maintained by the exchange of control information. Likewise, current methods also tend to result in control channel congestion since they require excessive utilization of radio resources due to the fact that session initiation protocol control messages are designed for wireline use, and each time a control message is sent in order to set up, tear down, or maintain a multimedia session, a large exchange of signaling information will necessarily have to occur just to enable the flow of such information.
Accordingly, what is needed is a more efficient method and apparatus for the interchange of session initiation protocol signaling messages between a mobile station and a network for setup of multimedia calls by the mobile station.